Retrofit light emitting diode tube

ABSTRACT

An LED light tube for replacement for fluorescent light tubes includes an elongated cylindrical transparent envelope, a base cap at each end of the envelope, and at least one LED device in electrical communication with the base cap. The LED light tube is adapted for use in troffer light fixtures.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional of U.S. patent application Ser.No. 09/998,274, filed on Nov. 30, 2001.

BACKGROUND OF THE INVENTION

[0002] The present disclosure relates to light bulbs and in particular,to light bulbs comprised of light emitting diodes.

[0003] There are millions of light fixtures installed and being producedeach year to provide both task and general lighting within schools,offices, homes, marine vessels, aircraft and the like. In recentdecades, more and more of these applications have been addressed withthe use of a fluorescent lamp as the light source. The advent offluorescent lighting has been shown to be a significant improvement overincandescent light fixtures. Noted advantages are numerous and include amarked reduction in energy consumption for a given light output, reducedoperating temperatures and a “cooler” light rendition index.

[0004] Fluorescent lamps are generally characterized as low-pressure arcdischarge lamps. A conventional fluorescent lamp commonly used introffer fixtures is shown in FIG. 1. The fluorescent lamp 10 includes anelongated envelope 12, whose internal wall is coated with a phosphor 14,and an electrode structure 16 at each end of the envelope. The envelope10 also contains a quantity of an ionizable material 18, such asmercury, and a fill gas at low pressure. The fill gas can be, forexample argon or krypton, or a mixture of these and other gases. Eachelectrode structure 16 includes a stem 20 having a tubulation 22 thereinthrough which the envelope 10 is exhausted. Leads 24 and 26 are mountedon the stem 20 and pass through the stem for connection to terminals 28and 30 disposed in an end cap 32. A cathode or filament-cathode 34 isconnected across each pair of the leads 24 and 26. A voltage, usuallysupplied by a ballast transformer, is applied across the electrodes toionize the ionizable material in the presence of the fill gas. Theresultant ionization and recombination of ions and electrons producesradiation that interacts with the phosphor coating to produce visiblelight.

[0005] Fluorescent lamps of a given length and type generally do notvary greatly in the electrical power consumed. In the past, mostattempts to change the power consumption have been in the direction ofincreasing the electrical energy requirements to produce a greater lightoutput. However, due to the increasing cost of purchasing electricalenergy, it is becoming increasingly desirable to reduce lighting loadsin existing facilities. Various ways of doing this include the use oflower wattage light fixtures, the elimination of lamps from certainareas, and the reduction of the number of lamps used in a given area.

[0006] Although fluorescent lamps have numerous advantages relative toincandescent sources, these lamps still suffer from a number ofdisadvantages. For example, the ionizable material and fill gases usedto generate the illumination pattern are relatively hazardous materials.Care must be taken to dispose of the fluorescent light fixtures to avoidreleasing these materials into the environment. Moreover, fluorescentlamps require the use of a ballast transformer to cause the fluorescentlamps to illuminate. Ballasts frequently fail and require replacement.Moreover, as noted above, the energy costs for operating fluorescentlamps need further improvement.

[0007] Accordingly, there remains a need for improved light sources thatmaintain the advantages incurred with the use of fluorescent lamps yetovercomes the disadvantages with this technology.

SUMMARY OF THE INVENTION

[0008] Disclosed herein is a retrofit LED light tube for replacing afluorescent light tube in a troffer fixture. The retrofit LED light tubegenerally comprises an elongated cylindrical transparent envelope; abase cap at each end of the envelope, wherein the base cap comprises afirst prong and a second prong extending from the base cap such that thefirst and second prongs are adapted to electrically communicate with afluorescent light socket; and at least one LED device in electricalcommunication with the base cap, wherein a positive terminal of the LEDdevice is in electrical communication with the first prong and anegative terminal is in electrical communication with the second prong.

[0009] In another embodiment, the LED light tube comprises an LED lighttube for replacement of a fluorescent light tube, the LED light tubecomprising: an elongated, cylindrical transparent envelope; a base capat each end of the envelope, wherein the base cap comprises a firstprong and a second prong extending from the base cap; and at least oneserial string of LEDs in electrical communication with the base caphaving circuitry means for connection with an AC source through anondissipative voltage dropping element, wherein each one of the atleast one serial string of LEDs are connected in parallel with the otherand are enclosed in the envelope.

[0010] The LED light tube can be used as a replacement for fluorescentlight tubes employed in troffer light fixtures. The troffer LED lighttube fixture comprises a housing and a tube holder. The tube holdercomprises electrical sockets in electrical communication with the LEDlight tube. The electrical sockets are adapted to receive a first andsecond prong in the end cap of the LED tube for supporting and providingelectrical power to a serial string of LED devices disposed in the LEDlight tube.

[0011] Other embodiments of the invention are contemplated to provideparticular features and structural variants of the basic elements. Thespecific embodiments referred to as well as possible variations and thevarious features and advantages of the invention will become betterunderstood when considered in connection with the detailed descriptionand drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Referring now to the figures, which are exemplary embodiments,and wherein the like elements are numbered alike:

[0013]FIG. 1 is a plan view of a conventional fluorescent light bulb;

[0014]FIGS. 2A and 2B are a perspective view and an end view of atroffer fixture including an LED light tube;

[0015]FIG. 3 is perspective view of another LED light tube;

[0016]FIG. 4 is perspective view of another LED light tube;

[0017]FIG. 5 is perspective view of another LED light tube;

[0018]FIG. 6 is perspective view of another LED light tube;

[0019]FIG. 7 is perspective view of another LED light tube;

[0020]FIG. 8 is a schematic of a ballast conversion circuitry utilizingvoltage reduction circuitry and frequency reduction circuitry; and

[0021]FIG. 9 is an electrical circuit diagram in schematic form forconverting AC voltage to a suitable DC voltage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present disclosure is directed to a solid-state lampemploying light emissive diodes (LEDs) that are designed as areplacement illumination source for fluorescent lamps. The solid-statelamp, hereinafter referred to as a retrofit LED light tube, may beconfigured as a replacement for a variety of fluorescent lightingapplications. In a preferred embodiment, the LED light tube is adaptedfor use in so-called troffer-type fluorescent lighting fixtures.

[0023] Referring now to FIGS. 2A and 2B, there is shown a trofferfixture assembly 100 suitable for use with the retrofit LED light tube.The troffer assembly is exemplary only, other troffer assembliessuitable for use will be apparent to those skilled in the art in view ofthis disclosure. The troffer fixture assembly 100 includes a square orrectangular housing 102 typically used with one or more fluorescentlight bulbs. The housing 102 comprises a substantially planar body andoptional sidewalls depending from the body portion along opposed edgesof the planar body portion. The troffer fixture assembly 100 is affixedonto or recessed in a surface such as a ceiling and consists of thehousing 102 with a clear, translucent glass or plastic lens (not shown)on the face thereof. The use of the lens is optional. The housing 102 ispreferably fabricated from sheet metal and includes an electrical troughadapted to accept electrical wiring from an external AC power source.Between the housing 102 and the lens, if present, is the main tubeholder. Electrical sockets 104, 106 are disposed and aligned at each endof the main tube holder. The sockets 104, 106 mechanically andelectrically communicate with the LED light tubes. As shown, theelectrical sockets 104, 106 include prong holders 108, 110 that areadapted to receive corresponding prongs extending from the light tube.The troffer fixture assembly 100 may further include a reflectivematerial disposed on a surface about the LED light tubes to redirect thelight downwards through the lens and maximize light output efficiency.Since the intended use of the LED light tubes are for replacement offluorescent light tubes, the troffer fixture may further include aballast transformer. As will be discussed in further detail below, theballast transformer may be removed, or bypassed during operation of theLED light tube.

[0024]FIG. 3 illustrates an LED light tube, generally designated 120.The LED light tube 120 generally comprises a cylindrical elongatedtransparent envelope 122, at least one serial string of LEDs 124 and acap 126, 128 at each end of the envelope 122. Each end cap 126, 128 isadapted for insertion into sockets 104, 106. For example, the end cap126, 128 can include two prongs 130, 132 for installment in the lighttroffer fixture 100. The prongs for a selected one of the end caps,e.g., 126, are fabricated from conductive materials and provideelectrical communication from a power source to the serial string ofLEDs. The prongs of the other end cap e.g., 128, serve to providemechanical support to the tube when the tube is installed the socket104, 106. Preferably, the other end cap, e.g., 128, is preferablyfabricated from non-conductive materials or is not in electricalcommunication with the LEDs. Alternatively, the end caps 126, 128 may beadapted to electrically and mechanically communicate with other types oftroffer electrical sockets. Each end cap 126, 128 further provides amechanical closure for each end of the envelope 122.

[0025] The LEDs and attendant circuitry are preferably disposed withinthe envelope 122. The circuitry may include a circuit board disposed inthe end cap (not shown) for converting AC voltage to the appropriate DCvoltage. The LEDs may be interconnected with a single 140 or a pair ofrigid, conductive wires 140, 142 electrically connected to the circuitboard. The circuit board is then electrically connected to the prongs inone or both of the end caps depending on the design. In the case wherethe circuit board is connected to one end cap, the LEDs can be connectedto the other endcap for providing support. Where only one rigid wire 140is utilized, the second wire 142 is referred to as the control wire 142.These wires 140, 142 provide both the mechanical support for the LEDs aswell as a voltage path from a power source. The individual LEDs areelectrically affixed to the wire mechanically using common solderingtechniques or the like. Each LED affixed to the wire has two electricalconnections, i.e., a positive and negative terminal connected to thewire 140. In the case of the dual fixed wire design, the positive leadfrom each LED is connected to one wire 140 and the negative LED lead isconnected to the other wire 142. Where more than one series of LEDcircuits are employed, the additional series of LEDs may be connected inparallel or in series with non-conductive materials. For example twoserial strings of LEDs can employ non-conductive sleeves into which theends of each opposing string is pressed. In this case, separate voltagesource lead wires would be incorporated that lead back to the commonvoltage source connected to the end cap as previously described. Avariation on this design would allow the LED strings to be twistedlengthwise to create a helix effect for more uniform light distribution.

[0026] As shown in FIG. 4, another embodiment in which the LEDs may beinterconnected includes soldering each individual LED 124 to provideelectrical communication to an adjacent LED 124′. The LEDs areconfigured with an appropriate number of LEDs allowed for a specificinput voltage. For simplicity, each set of voltage source specific LED'sis referred to as a string. The interconnected LEDs can then be securedto a fixed or semi-fixed plastic sleeve or holder that is slottedlength-wise. In this manner, proper spacing of the LEDs is maintained.The wires are extended back to the voltage source contained in the tubeend or end-caps.

[0027] Another embodiment in which the LEDs may be interconnected isshown in FIG. 5. In this embodiment, the envelope of LED light tubecomprises a two complementary half round pieces 150, 152 that when matedtogether form a cylindrical envelope. In each half-round piece 150 or152, a series of pockets slots, snaps and/or channels 154, 156respectively, are formed such that the required number of LEDs aredisposed in the into the respective pockets, slots, snaps and/orchannels along the length of the half tube base. A conductive wire isconnected to the LEDs to provide a control voltage. The ends of the wireare connected to voltage tabs or pins that are connected to theconductive leads connected to the external voltage source. The secondhalf-round 152 piece is then pressed onto the base half-round piece 150.The two halves 150, 152 are fastened together using either, snaps orslots built into the injection mold, glue, or other mechanical meanssuch as sliding the end caps over each envelope end of the combined tubehalves

[0028] Alternatively, the serial string of LEDs may be fabricated sothat the string can flex. In this manner, the serial string of LEDs canbe adapted for use in a variety of applications and may also beconfigured for maximum light output. For example, the LED light tube maybe fabricated to replace circular fluorescent light fixtures.

[0029] Referring now to FIG. 6, an elongated circuit board 160 can beused for mounting the LEDs 162. The circuit board 160 may then be slidinto the envelope 130 and connected to the end caps 126, 128 forproviding a source of power.

[0030] Alternatively, the LEDs could be mounted on a plurality ofcircuit boards 170 adapted to be attached substantially perpendicular tothe elongated wall of the envelope as shown in FIG. 7. A support 172 maybe utilized to support the circuit boards 170. A series of the circuitboards 170 would then be spacedly stacked within the envelope 130 sothat a series of the circuit boards 170 are deployed through a portionof the length of the tube. The LEDs may be mounted on the circuit boardat the outer periphery or mounted on one or both surfaces. Theindividual LEDs may further be splayed at angle with respect to thecircuit board 170 to produce the desired light pattern.

[0031] For installation in troffer fixtures 100, wherein the ballasttransformer is removed and/or bypassed, it is preferred that thecircuitry schematic shown in FIG. 8 is employed. An AC voltage 180 isapplied to the ballast 182, if present in the circuit. The ballast iscoupled a capacitor 184. The capacitor 184 is used as a reactiveimpedance to act as a current limiting source to the LEDs. A movistor,more commonly referred to as a varistor, may be utilized to provideadditional transient suppression to protect the LEDs from a transientsurge, especially when the LED light tube is first turned on. Thecircuitry schematic further includes a bridge rectifier 186, e.g., afull wave or half waver rectifier, for rectifying the incoming ACvoltage to a DC voltage. The bridge rectifier 186 may comprise a singlesolid-state device or a plurality of discrete diodes connected inseries. A frequency converter 188 then converts the DC voltage to anacceptable frequency for operating the LEDs.

[0032] The number of LEDs employed will vary with the intended lightingapplication and the value of the rectified DC voltage, whereinoptimization of such is well within the skill of those in the art. Forexample, suitable light emitting diodes operate at about ±2.0 Vdc suchthat if the input (rectified) DC voltage is 24 Volts, then a series of12 light emitting diodes may be combined to achieve the proper voltageapplication. If more light output is desired, additional strings oflight emitting diodes may be connected in parallel. One skilled in theart will recognize that additional circuitry for the strings will berequired, e.g., capacitors, resistors, bridge rectifiers, varistors,diodes and the like.

[0033] Alternatively, a suitable electrical circuit diagram in schematicform for converting AC voltage to a suitable DC voltage is shown in FIG.9. In operation, an AC voltage 200 is applied to the circuit. It shouldbe understood by those skilled in the art that the voltage can vary. Forexample, the voltage could be 120 volts with a 60 hertz frequency as isstandard in the United States, or could be 220 volts with a frequency of50 hertz as is standard in some other countries. The AC current firstpasses through a capacitor 202. Preferably, the capacitor is anonpolarity type capacitor wherein the capacitor functions by loweringthe amount of voltage passing through the circuit. Those skilled in theart will appreciate that the amount of capacitance is a function of theamount of LEDs in the circuit and incoming voltage levels. The currentthen passes through a rectifier 204 for converting the attenuated ACcurrent to a DC current. The rectifier can be a rectifier diode, abridge rectifier or any other rectifier that is suitable for convertingthe incoming AC voltage to DC and will be apparent to those of ordinaryskill in the art in view of this disclosure. Preferably, a full waverectifier is used. The DC current then passes through a filteringcapacitor 206. The filtered DC current is then used to illuminate theLEDs 208, shown arranged in series. One skilled in the art wouldappreciate that the LEDs could be arranged in parallel.

[0034] For installation in troffer fixtures 100, wherein the ballasttransformer is not removed and/or bypassed, additional circuitry ispreferably added to address the VAC generated by the ballast. Forexample, typical ballasts generate about 600 to about 750 VAC on itssecondary windings and create frequencies on the order of about 20,000to about 30,000 cycles. Consequently, the circuitry preferably includesmeans for reducing the input voltage, e.g., voltage reduction devicessuch as an electromechanical transformer, solid state rectifiers or thelike, for reducing the ballast output voltage to the range of about 120VAC. Moreover, in the case of electronic ballasts, the circuitrypreferably includes a means for reducing the ballast output frequency toabout 50 to about 60 cycles. Thus, depending on the type of ballast, thecircuitry may include voltage reduction circuitry and/or frequencyreduction circuitry.

[0035] Each LED is a semiconductor PN junction diode that, when forwardbiased, emits light at a wavelength that is a function of its materialand dopants. For instance, a crystal structure of gallium arsenide(GaAs) permits nonvisible infrared emission. Phosphorous added to GaAsforms gallium arsenide phosphide (GaAsP) and shifts the emission to thevisible red region whereas gallium phosphide (GaP) emits in the red,yellow and green regions. The present disclosure is directed to the useof LEDs that emit light, preferably, in the visible spectrum. Thecrystal structure for the LED is not intended to be limited to anyparticular type or wavelength emission. For example, LEDs of variouswavelengths without special light dissipating optics are commerciallyavailable at various wavelengths and light intensities from numeroussources such as those available from Hyosh Company in Japan. It shouldbe understood that LEDs with special light dissipating optics or speciallight reflecting optics would work. Moreover, it should be understoodthat organic LEDs (OLED) can be used. OLEDs are known to emit higherintensities of light and may be preferred in some applications where thehighest possible light intensities are important. However, the cost isgenerally higher for these specialized LEDs and since the user isgenerally concerned with cost these LEDs are less preferred.

[0036] The present disclosure advances the technology of lightingachieved through both incandescent and fluorescent lamp technology bysignificantly improving the energy saving qualities currently available.Energy savings on the order of 50% are easily achieved over mostfluorescent applications. Moreover, a significant reduction in heatgeneration by LED light tube over fluorescent is greater than about 80%with some LED light tube designs operating within +10% of the ambienttemperature of the surrounding environment. These significant decreasesin heat generation can have a significant impact on cost, size andduty-cycles required of air handling equipment employed withinthe-subject environment. Moreover, given the small size of theindividual LED light tube employed in this design (typically 3 mm-5 mmin diameter), the design possibilities for light fixtures that wouldutilize this light source are increased significantly. For example, therequirement of both fluorescent and incandescent lamps to incorporatesome sort of closed envelop to contain the required gasses to causeillumination are not necessary. The necessity for employing fragileglass or ceramic materials in a clear, translucent or semi-opaqueconfiguration is also eliminated. The elimination of these featuresallows for the construction of light fixtures employing the LED lightsource with more economical and stronger materials, such as the use ofplastic materials. Moreover, the LED light source eliminates the needfor employing environmentally harmful gases to achieve the light arcsince the LED lamp is a solid-state device.

[0037] While preferred embodiments have been shown and described,various modifications and substitutions may be made thereto withoutdeparting from the spirit and scope of the invention. Accordingly, it isto be understood that the present disclosure has been described by wayof illustration and not limitation.

What is claimed is:
 1. An LED light tube for replacement of afluorescent light tube, the LED light tube comprising: an elongated,cylindrical transparent envelope; a base cap at each end of theenvelope, wherein the base cap comprises a first prong and a secondprong extending from the base cap; and at least one serial string ofLEDs in electrical communication with the base cap having circuitrymeans for connection with an AC source through a nondissipative voltagedropping element, wherein each one of the at least one serial string ofLEDs are connected in parallel with the other and are enclosed in theenvelope.
 2. The LED light tube of claim 1, wherein the at least oneserial string of LEDs comprises a plurality of organic light emittingdiodes.
 3. The LED light tube of claim 1, wherein the at least oneserial string of LEDs comprises spacedly stacked circuit boards, whereineach one of the circuit boards include a plurality of serially connectedLEDs mounted thereon.
 4. A troffer LED light tube fixture comprising: ahousing comprising a tube holder, wherein the tube holder compriseselectrical sockets adapted to receive and electrically communicate anLED light tube; and an LED light tube disposed in the tube holder,wherein the LED light tube comprises an elongated, cylindricaltransparent envelope, a base cap at each end of the envelope, whereinthe base cap comprises a first prong and a second prong extending fromthe base cap, and at least one serial string of LEDs in electricalcommunication with the base cap having circuitry means for connectionwith an AC source through a nondissipative voltage dropping element,wherein each one of the at least one serial string of LEDs are connectedin parallel with the other and are enclosed in the envelope.
 5. Thetroffer light fixture according to claim 4, wherein the housing furthercomprises a reflective material disposed on a surface of the housing formaximizing the light output.
 6. The troffer light fixture according toclaim 4, wherein the at least one serial string of LEDs comprises aplurality of organic light emitting diodes
 7. The troffer light fixtureof claim 4, further comprising a means for protection against a voltagesurge.
 8. The troffer light fixture of claim 7, wherein the means forprotection against a voltage surge comprises a varistor positioned inparallel with the at least one serial string of LEDs.
 9. The trofferlight fixture of claim 4, further comprising a ballast transformer andmeans for bypassing the ballast transformer.
 10. The troffer lightfixture of claim 4, wherein the means for bypassing the ballasttransformer comprises a voltage reduction circuit and frequencyreduction circuit.